A number of techniques have been considered for displaying three dimensional (3D) imaging using video transmission. For non-holographic techniques, this requires projecting different (stereoscopic) images to the left and right eyes. Many of these techniques require the use of special glasses to project the two images to the two eyes. Recently, techniques that don't require the use of the special glasses have been developed. One approach developed by Dimension Technologies, Inc. (DTI), a company located in Rochester, N.Y., involves the use of parallax illumination. This approach is discussed in detail in "3D Without Glasses", by I. Eichenland and A. Morris, Information Display 3/92, Pages 9-12. This article describes one such display device in which an ordinary monochrome or color liquid-crystal display (LCD) is located in front of the viewer. The LCD is a two-dimensional array of individually controllable elements (pixels) arranged in rows and columns, typically 640 columns and 480 rows in an 8.times.6-in. active area. It is illuminated from behind, and the amount of light transmitted by the individual pixels can be controlled so that images with a range of gray shades can be displayed.
To generate 3-D images, the LCD displays the left and right halves of a stereopair on alternate columns of pixels at a rate of 30 frames per second, the standard rate of NTSC television. For example, the left image appears on the odd columns, and the right image appears on the even columns. Thus, each complete stereoscopic image consists of 320 columns and 480 rows.
In this display, both halves of a stereopair are displayed simultaneously through the use of a special illumination plate located behind the LCD, which optically generates a lattice of 320 very thin, very bright uniformly spaced vertical light lines. The lines are spaced with respect to the pixel columns, and because of the parallax, the left eye sees all of these lines through the odd columns of the LCD, while the right eye sees them through and even columns. Such structures are further explained, for example, in U.S. Pat. Nos. 5,457,574, 4,829,365, 4,717,949, 5,036,385, 5,040,878, 5,410,345 and 5,500,765, the specifications of which are all hereby incorporated by reference.
Although numerous modifications to the basic structure described above are disclosed in these references to provide greater image resolution, multiple viewing zones, and improved "look-around" capability, the displays disclosed in these references are either entirely three-dimensional or two-dimensional at any given time. However, in many applications, it would be desirable to be able to display two-dimensional and three-dimensional images on the display simultaneously. Further, it would also be desirable to be able to more (i.e., drag) and/or enlarge or diminish the display area for such 3D images on the display.
Additionally, in such displays, there is a fixed relation between the distance between the LCD and the illumination plate and the viewing distance (display to viewer) that determines (in part)the dimensions of the "viewing zones". These viewing zones are the regions in front of the display where the observer can perceive 3D images. Consequently, if the position of the viewer's head is not at an appropriate location with respect to the screen and the light line, the eyes do not see different images and the 3D effect will be gone.
Different head tracking devices have been employed to track head movement and solve this problem. For example, U.S. Pat. No. 5,457,574, describes employing multiple lamp illumination systems which are used to allow a smooth stereoscopic image tracking as the head of the observer move laterally (see for example FIG. 7A, 7B of this patent). A similar scheme can be used to implement a "look around" feature in which the observer would be able to see different perspectives of the object as he moves his head. This is achieved by timing appropriate stroboscopic lamps.
Present implementations of parallax illumination concepts are bulky with a large number of lamps or moving elements for head tracking that require precise alignment. Because of this, the size becomes unwieldy, and the reliability of the display suffers.